The article examines the insufficiently explored domain of Russian verbal word formation synthesis — the lacuna (gap) field. For the first time ever, the term «lacuna (gap) modification» is being introduced into linguistic usage. This new term is defined, the well-grounded classification of lacuna types is presented, and the methods for creating an adequate lexicographic index of lacunas (gaps) is provided. Using the methods of componential analysis and synthesis, the lacuna charts and diagrams for the verbs of sound are constructed. Data obtained from the Russian native speakers' questionnaire is used for clarification purposes. The results of the research set forward the identification methodology and consistent description techniques for lacunas (gaps) with respect to their future codification in various dictionaries, e.g., thesaurus, word-formation, etc.